1. Field of the Invention
This invention pertains to blood pressure monitoring apparatus employing a catheter placed in the artery. The pressure in the artery may be displayed as a waveform, digital readout, or permanently recorded on a strip chart at a monitor. This apparatus is found in the general class of SURGERY. This invention shows a tube system from a supply system for automatically preventing the presence of unwanted air bubbles from the catheter to a monitor. This air may intially develop in the connectors or tubing connected to the supply tube leading to the catheter. The present device uses a filter to block air from the supply system to the pressure transducer.
2. Description of the Prior Art
Physiological pressure measuring and monitoring of arterial blood has been used for many years. This procedure uses a catheter whose end is inserted into an artery of the patient. This catheter, with support tubing, stopcocks, continuous flush device, domes, etc., connects the arterial blood with a pressure signal transducer through a fluid path. The transducer converts the hydraulic pressure into electrical signals which are sent to the monitor. The monitor converts these signals into visual waveforms, numerical values and/or permanent records using strip charts. The fluid path for conducting hydraulic pressure signals is continuous from the catheter to a diaphragm within the dome of the transducer. This diaphragm, which is a portion of the transducer, is physically responsive to the hydraulic pressure and its variations within the fluid system. The transducer is able to detect these pressures and their variations through the diaphragm and transmit them in electrical form to the monitor.
When an artery of a patient is "invaded," the natural defense mechanism for preventing infection is violated. Hence, it becomes extremely important that the entire blood pressure monitoring system be initially sterile and their sterility maintained during the procedure. This includes all fluid connections, surfaces and components in contact with the blood system.
Many symposiums, conferences, papers and articles have been directed toward problems of less than satisfactory waveforms or results. A primary factor contributing to less than satisfactory results is overdamping, which is caused primarily by air bubbles in the system. Blood or thrombii left in the catheter following blood sampling may also contribute to overdamping. Air bubbles are also a major cause of lowering the resonant frequency of the system which, in turn, causes ringing or wave amplitude distortion. The size as well as location of air bubbles is significant with respect to their effect on the waveform. With a given size, an air bubble when close to the transducer in the tubing system may result in a lowering of the resonant frequency from ten to twenty Hertz.
As noted above, the compressible nature of air bubbles in the fluid conductor also diminishes and otherwise degrades the hydraulic signal to the diaphragm of the pressure tranducer. Trandsucers have been known, for example from U.S. Pat. Nos. 2,841,984; 4,072,056 and 4,252,126. These last two patents were directed to use in the recording of hemodynamic pressure in an artery. Of particular note is U.S. Pat. No. 4,365,635 which shows a special dome construction for removing entrapped air. A major problem associated with that system is that it does not provide for elimination of air once the transducer has been hooked up to the dome.
U.S. Pat. No. 4,252,126 describes a transducer dome in which the filter or diaphragm is carried so that any accumulation of bubbles after the unit has been brought to operating condition is not vented.
The present apparatus provides a supply of fluid from a bag supply through a flexible tube leading from this supply. This tube may include a flushing device, one or more entry cocks which are adapted for adding of drugs in liquid form, and connection to a catheter which is placed in a patient. In one embodiment, this infeed line is flow-connected to a second tube conductor which carries the pressure variations through this fluid to the pressure transducer. At the entrance to this second line, an in-line hydrophilic filter prevents any air to flow into the second line and pressure transducer. The positive elimination of air bubbles in the second line to the pressure transducer is not shown in prior art above or known to the Applicant.
In an alternate embodiment, an in-line hydrophilic filter is provided at the fast-flushing device and this filter is before and in way of a conducting fluid line which is filled with fluid and purged so that this fluid line leads to a transducer. This alternate device is specifically adapted to be used with present blood pressure appparatus so as to provide an air-free conductor.